Old mine pits might help wind farms

The big shortcoming of wind power is that breezes don't always blow when electricity is needed most.

Now, a solution to that supply-and-demand problem may have been found -- in abandoned ore pits on the Iron Range.

Researchers in Minnesota said Wednesday that 10 former mining sites could potentially be developed into pumped-storage hydroelectric projects that would make it possible, in effect, to save power from wind farms.

"There is no doubt of the possibility of developing something like this," said Donald Fosnacht, lead researcher on the project for the University of Minnesota-Duluth's Natural Resources Research Institute (NRRI).

Pumped-storage is a bit like recharging a battery. At night, when electric demand is low, excess power is used to pump water from a low-lying reservoir to a higher-elevation pool. During the day, as demand rises, water from the upper pool is released, generating hydroelectricity and refilling the lower pool.

Wind farms produce significant amounts of power at night when it's less needed. Finding ways to store wind power has been a major challenge for the industry.

"This is a promising way of doing it," said Rick Lancaster, vice president for generation at Great River Energy, which participated in the study. "It doesn't involve burning any fuel. It takes electricity off the grid, uses it to pump water uphill and then you have the energy of the hydropower. It has a lot of things going for it."

Great River Energy, the Maple Grove-based wholesale power cooperative that serves 650,000 rural and suburban customers, and Minnesota Power, whose 146,000 customers include the taconite mines, contributed engineering help and $10,000 each to the Iron Range study. The U's Initiative for Renewable Energy and the Environment underwrote most of the research.

Both utilities rely partly on wind power and have been interested in pumped storage, but don't have definite plans for any projects. Even so, Lancaster said that Iron Range pumped storage could be an important option in the future.

The technology is used at 40 U.S. locations, often to balance out low-demand periods of nuclear power plants, said Fosnacht, who is director of NRRI's Center for Applied Research and Technology Development.

At a site near Virginia, Minn., researchers estimated that a 160-megawatt pumped-storage project could be built for about $120 million. That's about the output of modest-sized generator burning natural gas.

But a hypothetical cost analysis by researchers suggested that pumped-hydro would be more expensive than natural gas generation. Natural gas prices have dropped significantly thanks to increased exploration using new drilling methods.

The research team, which included scientists from the U's St. Anthony Falls Laboratory and the Humphrey School of Public Affairs, examined 47 old mining areas, looking for places where an upper reservoir could be at least 300 feet above a lower pool. Fosnacht said feasibility studies would be needed before proceeding with projects on any of the 10 potential sites.

Though the Iron Range is far from most of the Midwest's wind farms, Minnesota Power already has the capacity to move electricity on a 465-mile transmission line from North Dakota to its service territory, the study said.